Hepatitis B virus (HBV) infection is one of major global health problems.1 Although primary HBV infections in most adults are self-limited, 3-5% patients do not resolve and develop into chronic infection and this rate is much higher among young children infected with HBV.2 The estimated number of the chronic hepatitis B (CHB) carriers is approximately 350-400 million worldwide, with more than one million deaths annually resulted from cirrhosis, liver failure and hepatocellular carcinoma.2 
Agents currently available for the treatment of HBV infection can be classified into two main categories: immunomodulator and nucleoside/nucleotide analogues. Although the efficacy of INF α, a representative immunomodulator, has been established by a numerous studies, the clinical application of INFα has been compromised by the low overall response rate, side effects and high cost.3,4 Nucleoside/nucleotide analogs, on the hand, continue to dominate the anti-HBV therapy. There are at least six nucleosides/nucleotides in the clinical use, including lamivudine (Epivir-HBV®, GlaxoSmithKline), adefovir dipivoxil (Hepsera®, Gilead), entecavir (Baraclude®, Bristol-Myers Squibb), telbivudine (Tyzeka®, Idenix/Novartis), clevudine (Levovir® in South Korean, Phase III in US, Bukwang/Pharmasset) and most recently tenofovir (Viread®, Gilead). (FIG. 1). These agents significantly suppress the replication of HBV DNA to a lowest possible level which leads to the favorable clinical outcomes and prevents advanced liver sequelae. Indeed, the introduction of these oral nucleosides/nucleotides is the breakthrough in the anti-HBV therapy. It has been reported that the number of patients in US registered for liver transplantation has been decreased 30% since widespread application of nucleoside anti-HBV agents.5 
There is no solid evidence that current nucleosides/nucleotides treatments have direct effect on the HBV covalently closed circular DNA (cccDNA), which has a long half-life and is believed to serve as the transcriptional template as long as the termination of the therapy,6 leading to the viral DNA rebound. Consequently, long-term, highly effective antiviral therapy may be required to prevent viral relapse following discontinuation of the treatment.7 Unfortunately, long-term nucleosides/nucleotides treatment is always associated with the development of drug-resistant mutants which significantly compromised the efficacy. The nature of HBV polymerase coupled with high replication rate lead to the emergence of HBV mutants which have survival advantage in the presence of certain antiviral agents.8 The current use of lamivudine, the first approved anti-HBV nucleoside, has been limited by the high frequency of lamivudine resistance (most commonly rtL180M±rtM204V/I). The in vitro study indicated rtL180M+rtM204V/I mutations result in a >1000-fold decreased susceptibility of the virus to lamivudine without significant impairing of polymerase function.9,10 In clinical practice, the approximate rate of resistance of lamivudine is about 20% at the end of 1-year and 70% after 5-year treatment.11-14 Telbivudine, another L-nucleoside, is cross-resistant to the major lamivudine mutation at YMDD motif, represented by the rtM204I. It is associated with a lower rate of resistance compared to lamivudine after 1 year therapy (around 5% in HBeAg-postive patients), while the rate jumps to 22% after 2 years.15 These data may indicate a possible high rate of drug-resistance in the longer duration of telbivudine therapy. Adefovir belongs to the acyclic phosphonate. Bearing distinct acyclic sugar moieties, this nucleoside is not cross-resistant to the L-nucleosides. However, there are two primary adefovir-resistant mutations at codon 181 (rtA181T) and codon 236 (rtN236T) which result in two-fold to nine-fold increase in median effective concentration.16-18 Although the fold of increase is modest, reports showed non-response to the adefovir treatment is associated with three patients who developed a mutation.19,20 The rate of developing resistance with adefovir treatment is also significant high, with about 3% at 2 years and 29% at 5 years.21 The other potent anti-HBV nucleoside, entecavir, has a high genetic barrier to resistance. However, in patients with pre-existing lamivudine-resistant mutations, the probability of entecavir resistance increases from 1% at 1 year to 51% to 5 years.22,23 Therefore, entecavir is not recommended as monotherapy in patients with YMDD mutations. Although there is no solid evidence of detecting resistance to date after continuous treatment with tenofovir or clevudine in clinical, results after prolonged therapy remain to be determined.
The development of antiviral resistance is generally associated with worse clinical outcomes.8 For example, the efficacy of lamivudine treatment was negated by the development of drug resistance.24 Patients who developed drug resistance were less likely to demonstrate histological improvement (44% versus 77%) and more likely to show liver deterioration (15% versus 5%) in comparison to subjects who have no evidence of drug resistance.24 Particularly, there have been reported hepatitis flares and hepatic decomposition in patients following the development of antiviral resistance.25 Therefore, a careful management of antiviral resistance is paramount in the anti-HBV treatment. Add-on (combination with different nucleosides or interferon) therapy and switching to an alternative nucleoside monotherapy are two major options for patients with suboptimal response to the initial single nucleoside treatment. Although it is not clear which is the most effective way in the management of resistance, providing additional/alternative agents with high genetic barrier and with different resistance profile from the initial drug are critical, Current anti-HBV arsenal is limited. Therefore it is important to develop novel nucleoside analogs which are active against not only wild type (WT) but also existing HBV drug-resistant mutants. During the course of our drug discovery programs, introduction of fluorine atom onto the sugar moiety generated a number of novel nucleosides with interesting biological interesting nucleosides.26-35 Therefore, it is of great interest to explore the substitution of fluorine atom on the carbocyclic nucleosides with an 6′-exo-cyclic alkene (6′-methylene). Herein, we would like to report the invention of the interesting fluorinated carbocyclic nucleoside which is active against HBV-WT as well as lamivudine- and adefovir-resistant mutants.
The search for antiviral agents treatment of Hepatitis B virus, Hepatitis C virus, Herpes Simplex virus I and II (HSV I and II), cytomegalovirus (CMV), Varicella-Zoster Virus (VZV) and Epstein Barr virus is an ongoing process and the present invention is directed to those viral disease states.